Windows RT Set-top Box.
Google has the Nexus Q
Apple has the Apple TV
The original Apple TV was released in 2007. It's currently in its 3rd iteration at the price tag of $99. Google on the other hand took almost four years to release a media streamer, the Nexus Q, which was ridiculously overpriced($299) for what it could do. I've never used a Google TV set-top box but from online reviews, it seems like it is a half-baked platform.
Since the cheapest Xbox costs $199, is it inconceivable for Microsoft to release a $99 set-top box running some variant of Windows 8?
Edited to replace WP8 with Windows RT.